The present invention relates to a control valve for a self-emptying centrifuge drum for draining closure fluid out of a closure chamber positioned below an axially movable piston slide with a valve piston that closes the closure-fluid runoff bores by means of centrifugal force and opens them by supplying control fluid to an initial control chamber that has an inlet and an outlet.
A control valve of this type is known, for example, from German Utility Model No. 7 306 879. Emptying the centrifuge drum is initiated by supplying control fluid to the control chamber through a control-water channel. The high fluid pressure produced by centrifugal force acts on the associated face of the valve piston and generates a force that is greater than the centrifugal force acting on the piston, moving it toward the center of the drum. This releases the closure-chamber runoff bores, the chamber empties, and the piston slide descends axially. To terminate the emptying process and close the piston slide it is necessary to stop supplying control water, upon which the control chamber empties through an outlet, the valve piston closes off the runoff bores again, and the piston-slide closure chamber fills up again.
Self-emptying centrifuge drums are preferably only partly emptied in order to optimize operations. To ensure unobjectionable removal of even heavy solids, the piston slide must stroke as far as possible. This is only possible, however, if the control valve operates very rapidly. Although the known valves open rapidly enough when the control-fluid supply is ample, closure depends on emptying the control chamber, which takes longer. The amount of solids extracted during each partial emptying should also be as constant as possible in order to minimize product loss and obtain compact solids. Since the time it takes to open and to close the slide piston with . . . the known control valve depends on how much closure fluid is supplied to the control valve and on how rapidly, it is often impossible to keep this figure constant.